Recently, the communication capacity keeps increasing in the field of information communication, and introduction of the wavelength division multiplexing (WDM) technique into core networks is examined. Introduction of optical communication into access networks is promoted, and various services requiring large capacities are provided more and more. At present, integration into packet routing-based networks is advancing. However, the packet transfer technique increases the delay amount and jitter amount (variations of the delay) for large amounts of video services, real-time services, and the like along with the expansion of the communication scale. As a result, the service quality degrades, and service contents are restricted.
To the contrary, the WDM technique, which uses wavelength paths for performing data communication using optical signals having unique wavelengths, can implement a large communication capacity, small delay amount, small jitter amount, and the like, and can solve the problems of the packet transfer technique. Hopes are running high for further development of the WDM technique in the field of information communication.
Together with introduction of the WDM technique into core networks, introduction of the WDM technique into metropolitan area networks and application of the ROADM (Reconfigurable Optical Add Drop Multiplexer) are also under discussion. The ROADM has a function of mainly gathering traffics in access networks, and connecting them to core networks. A relay optical node near a core network transits the gathered wavelength paths at high ratio without changing their wavelengths. Traffics between access networks will further increase because of P2P (Peer to Peer) and the like, and traffics loopback in metropolitan area networks are highly likely to increase further.
The WDM technique can handle only several hundred wavelength paths. Compared to a packet network in which a plurality of session flows can be virtually handled within the network, such an operation that a wavelength is permanently assigned to a service in a wavelength network would decrease the bandwidth utilization and raise the cost of equipment investment. It is expected that a larger number of services are multiplexed as the capacity of wavelength paths increases. A fault generated in the photonic physical layer may seriously affect a plurality of upper service layers.
Under the circumstance, a WDM technique capable of quickly responding to a demand, increasing reliability, and reducing the cost is expected. To meet this expectation, optical node apparatuses for a wavelength network and ROADM require flexible wavelength path setting capable of cooperating with an advanced control plane (CP), sophisticated functions, excellent expandability capable of small start, high utilizations for band (wavelength) resources and apparatus resources in wavelength networks, small size, low power consumption, and low operational cost. To satisfy these requirements, a variety of proposals have been made.
For example, Japanese Patent Laid-Open No. 2006-087062 (to be referred to as reference 1) discloses a node configuration which can add and drop wavelengths using photocouplers and wavelength selection switches. This configuration can expand apparatus resources in accordance with the number of routes. For a small number of routes or a small number of added/dropped wavelengths, the operation becomes possible with a minimum number of apparatus resources. Reference 1 also describes the arrangement of a wavelength multiplexer which multiplexes optical signals of individual wavelengths transmitted from individual Tx and transmits the multiplexed signal to a core unit, and the arrangement of a wavelength demultiplexer which demultiplexes a WDM signal from the core unit into individual wavelengths and receives them at Rx.
In this configuration, M×M matrix switches can input/output an optical signal to an arbitrary wavelength port of an optical multiplexer (optical demultiplexer). A permanent connection between the wavelength at Tx/Rx, the wavelength port of the optical multiplexer (optical demultiplexer), and the transmission/reception wavelength at Tx/Rx is canceled, optimizing Tx/Rx resources. FIG. 22 exemplifies the node apparatus described in reference 1.
The node apparatus shown in FIG. 22 includes optical branching couplers 2201, wavelength selection switches 2202 and 2203, wavelength multiplexer/demultiplexer units (AWG) 2204 and 2205, transponders 2206, and optical matrix switches 2212. The transponder 2206 transmits/receives a WDM signal 2207 and client signal 2208.
This node apparatus copes with four routes, i.e., transmission lines 1 to 4. WDM signals branched by the optical branching couplers 2201 are input to the wavelength selection switches 2202 which selectively multiplex wavelengths to other routes. At this time, each wavelength selection switch 2203 selects a wavelength to be dropped from the WDM signals branched by the corresponding optical branching coupler 2201, and inputs the selected Drop signal to the corresponding wavelength multiplexer/demultiplexer unit 2204.
Each optical matrix switch 2211 controls the switch so that a desired transponder 2206 receives a Drop signal demultiplexed by the wavelength multiplexer/demultiplexer unit 2204. Each optical matrix switch 2212 on the side of the wavelength multiplexer/demultiplexer unit 2205 controls the switch based on a WDM transmission signal from the transponder 2206 to select an input port of the wavelength multiplexer/demultiplexer unit 2205 that corresponds to the wavelength of the WDM transmission signal. The wavelength multiplexer/demultiplexer unit 2205 multiplexes WDM transmission signals from the subordinate transponder 2206. The wavelength selection switch 2202 selectively multiplexes the wavelengths of Transit wavelength path signals from other routes, and transmits the multiplexed signal to a corresponding route.
Reference: Japanese Patent No. 3533316 (to be referred to as reference 2) discloses the arrangements of a wavelength multiplexing transmission means and wavelength multiplexing reception means, and a switching operation to a spare optical transmitter or spare optical receiver when an optical transmitter and optical receiver fail.
In this arrangement, a spare optical transmitter and spare optical receiver can be made common to operating ones, reducing the cost and size of the system. If a fault occurs in an operating transmission line, a signal selection circuit in the wavelength multiplexing transmission means can change the wavelength multiplexer input port to switch the operating transmission line to a spare one.
Reference: “Highly Reliable Optical Bidirectional Path Switched Ring Networks Applicable to Photonic IP Networks”, Journal of Lightwave Technology, Vol. 21, No. 2, February 2003 (to be referred to as reference 3) describes a node apparatus having wavelength path switches, and a WDM ring network configuration using the node apparatus. Optical matrix switches and transmission lines which implement the wavelength path switches have redundancy, improving the reliabilities of the node apparatus and network. FIG. 23 exemplifies the node apparatus described in reference 3.
The node apparatus shown in FIG. 23 includes wavelength multiplexer/demultiplexer units 2304 and 2305, transponders 2306, 1×2 optical matrix switches 2307 and 2311, and optical matrix switches 2318 and 2319. The 1×2 optical matrix switches 2311 receive/output client signals 2313. This node apparatus copes with three routes, i.e., transmission lines 1 to 3. Hence, the wavelength multiplexer/demultiplexer units 2304 and 2305 are arranged by numbers corresponding to the three routes.
Similarly, the transponders 2306 are also arranged by a number corresponding to all WDM wavelengths for the respective routes. The client of the transponder 2306 is connected to the optical matrix switches 2318 and 2319 via the 1×2 optical matrix switch 2307. The optical matrix switch 2318 is used in an operating system, and the optical matrix switch 2319 is used in a spare system. When the operating system optical matrix switch 2318 fails, the 1×2 optical matrix switch 2307 switches it to the spare system optical matrix switch 2319. Although not shown in FIG. 23, the number of compatible routes and the number of accommodated clients can be increased by expanding the switching capacities (number of ports) of the optical matrix switches 2318 and 2319.